Manufacture of aliphatic acids, anhydrides, and ketones



Patented Nov. 7 24, 1.936

ANHYDRIDES, AND

KETONES Henry Dreyfus, London, England,

No Drawing. Application January 25, 1933,-Serial No. 653,475.v 1932 13Claims.

This invention relates to the manufacture of oxygen-containing aliphaticcompounds such as ketones, acids and anhydrides by thermal decompositionof metal salts of aliphatic acids, particularly of lower fatty acids,and more espe cially to the production of acetic acid, acetic anhydride,acetone or mixtures of such compounds by the thermal decomposition ofmetal acetates. Metal acetates yield on thermal decomposition aceticacid, acetone or both acetic acid and ace-v tone according to theparticular metal acetate employed. Thus, acetates of the highly basicalkali and earth alkali metals (e. g. sodium, potassium, barium andcalcium) and of lead yield acetone without substantial formation ofacetic acid, while acetates of such metals as aluminium,.

manganese, and zinc yield mixtures of acetic acid and acetone; andacetates of such metals as silver, mercury, copper, chromium, and nickelyield acetic acid with little or no acetone.

Further, I have described, in my U. S. application S. No. 609,252 filed,4th May, 1932, how acetic anhydride can readily be produced bythermally decomposing the acetates of metals of low basicity, inpresence or absence of normal salts of strong mineral acids,particularly when the acetates are employed in anhydrous orsubstantially anhydrous condition. As examples of metals of low basicitymay be mentioned copper, chromium,

tin, nickel. Again, in my U.,S. application S. No. 609,251 filed 4thMay, 1932, I have described how acetic anhydride can be produced bysimilarly treating acetates of highly or relatively highly basic metalsin admixture with normal salts of strong mineral acids. Moreover, in myU. S. application S. No. 631,101 filed 30th August, 1932, now Patent No.2,040,926 dated May 19, 1936 I have described how dilute acetic acid maybe ',concentrated to any desired degree by forming therefrom an acetateof a heavy metal and subjecting the acetate,-without completelydehydrating it, to thermal decomposition, whether or not in presence ofa normal salt of a strong mineral acid.

It has, however, .been found that when metal acetates are subjected tothermal decomposition as in the'processes above referred to, certaindifficulties are liable to arise in'practice. In particular, especiallywith heavy metal acetates, sublimation of 'the acetate or of partiallydecomposed acetate is liable to occur, resulting in loss of the productsof decomposition, acetic acid, acetone, acetic anhydride, and often toblocking of the apparatus with the sublimate. This difiiculty isespecially in evidence when local over-heating In Great Britain February9,

occurs or when the decomposition is performed in a stream of gas orvapour. Moreover, it has been found difiicult to obtain uniform heatingof the acetates, and that unless uniform heating is attained localover-heating and consequently 5 destructive decomposition of thereaction products is very liable to occur.

I have now found that such difliculties can readily be avoided and verysatisfactory decomposition to oxygen-containing aliphatic com- 1 poundsachieved if the acetates are subjected to the decomposition in admixturewith or suspension in high boiling diluents. As instances of suchdiluents may be mentioned high boiling hydrocarbons and high boilingethers, e. g. dibenzyl ether, plienyl benzyl'ether, diphenyl ether,naphthyl aryl ethers. In general inert liquids having boiling pointshigher than 250, and especially higher than 300 C., are very useful forthe purposes of the invention.

The invention may be applied to the production of acetic acid, aceticanhydride, acetone or mixtures of such bodies according to theparticular acetate and conditions employed. Thus, for instance, acetatesof metals of low basicity may be decomposed to yield acetic anhydride ormixtures of acetic anhydride and acetic acid, the acetates beingemployed in simple admixture with or suspension in the diluents, saltsof strong acids, e. g. sulphates, chlorides and the like also beingpresent if desired. Non-basic acetates ,of 30 copper, nickel andchromium are particularly useful for this purpose. Acetates of metals ofhigh or relatively high basicity in admixture with normal salts ofstrong mineral acids and in admixture with or suspension in the diluentsof the 5 invention may also be thermally decomposed to yield aceticanhydride or mixtures of acetic anhydride and acetic acid. In order toobtain the highest possible yields of anhydride, the acetates should beemployed in anhydrous or substantially anhydrous condition, i. e. freeor substantially free fromwater of crystallization, and when they aremixed with normal salts of strong mineral acids, such salts should alsobe employed in the anhydrous or substantially anhydrous condition.

The invention is not, however, limited to the employment of anhydrous orsubstantially anhydrous acetates, as I may eifect the decomposition inpresence of suflicient water to produce acetic acid without anyanhydride; thus I may employ heavy metal acetates which have not beencompletely dehydrated. Further, in cases where acetone or mixtures ofacetone and acetic acid are to be produced, acetates of suitable metalsmay be' thermally decomposed in admixture with or suspension in highboiling diluents according to the invention; for instance acetates ofaluminium,

manganese or zinc may be decomposed to yield mixtures of acetic acid andacetone, while acetates of the alkali or earth alkali metals may bedecomposed to yield acetone.

The thermal decomposition of the acetates according to the invention maybe effected in any convenient way. For instance, the acetates inadmixture with the diluents, and also, if desired, in admixture withnormal salts of strong mineral acids, may be simply heated. Preferably,however, they are heated in a current or stream of an indifferent gas,e. g. air, carbon dioxide, nitrogen or the like, or of an indifferentvapor, e. g. benzol or petroleum ether. The heating may be performed atany temperature sufficient to decompose the acetate, temperatures ofbetween about 200 C. and 450 C. being usually suitable for this purpose.Excessive temperatures liable to cause destruction of the anhydride,acid or acetone should, of course, be avoided. The decomposition may beeffected at ordinary atmospheric pressure or under pressures greater orless than atmospheric.

Preferably such diluents are employed as have boiling pointssufficiently high to avoid substantial evaporation during thedecomposition. Loss of diluent by distillation or evaporation may,however, be prevented or minimized by heating the acetate diluentmixture under reflux.

The invention is not restricted simply to the thermal decomposition, butembraces all processes and manufactures comprising the thermaldecomposition of acetates according to the invention. For instance, itmay be applied to the concentration of aqueous acetic acid, or to therecovery of concentrated acetic acid and/oranhydride from wasteacetylation liquors, as described in my U. S. applications S. Nos.609,251, 609,252 and 631,101, or to the manufacture of acetone fromacetates of more basic metals such as calcium acetate.

The preparation of more concentrated acetic acid and/or acetic anhydridefrom dilute industrial acetic acid forms a very important feature of theinvention. As above indicated, this may be effected by treatment of thedilute or waste acids to form suitable acetates, which acetates, whetheror not in admixture with nomal salts of strong mineral acids, afterremoval of water to the extent desired, are subjected to thermaldecomposition according to the invention. Preferably the dilute or wasteacids are treated with oxides, carbonates or other appropriate compoundsof metals of low basicity to yield the acetates, oxides or othercompounds of copper, nickel or chromium being particularly useful forthis purpose. The formation of the actates and the removal therefrom ofexcess water can be effected in any convenient way, as for instance bythe methods referred to in my U. S. application S. No. 631,101. Thus theoxides or other substances may be added to the acid liquor, preferablyat an elevated temperature and in stages. The salt formed may bepartially or completely separated from the solution by evaporation ofthe water; preferably however, the acetate is allowed to crystallize outon cooling, if necessary after partial evaporation of the water;frequently the separation may also be assisted by the addition ofanother and more soluble'acetate, or of an organic liquid in which thesalt is insoluble.

The acetates may be removed from the soluand may be recovered in a veryconcentrated tion by filtration, centrifuging, decantation, or in anyother way, and further adherent or combined water removed if desired, byheating; such water may, however, be removed in other ways. The acetatesmay be mixed with or suspended in the 5 high boiling inert diluents atany stage in the process, before or after the removal of adherent orcombined water. For instance, when acetates containing adherent orcombined water, part or all of which is to be removed before the acetateis decomposed, are separated from the liquors, such acetates mayadvantageously be heated in admixture with or suspension in diluentsaccording to the invention to remove water, before they are subjected tothermal decomposition.

While the invention has been described more particularly with referenceto the thermal decomposition of acetates, it is in nowise limitedthereto, but includes the thermal decomposition of salts of higheraliphatic acids and especially of other lower fatty acids in presence ofhigh boiling inert diluents. For instance, I may employ thecorresponding propionates or butyrates in place of the acetates toobtain the corresponding anhydrides, acids or ketones. Moreover, theinvention may be applied inter alia to the recovery of such anhydrides,acids or ketones from dilute or waste higher aliphatic acids.

The invention is illustrated by the following example, but it is ofcourse in no way limited thereby.

Example To 300 gallons of acetic acid of approximately 25%concentration, recovered from a cellulose acetylation, and heated to 80C. is gradually added 350 lbs. of cupric oxide. The solution is allowedto cool, whereupon copper acetate mainly in the form of thepenta-hydrate is separated out. This salt is then filtered off from themother liquor, and added to approximately its own weight of a petroleumfraction of boiling point between 290. and 330 C. The mixture is heatedto 90 C. to remove most of the water, and the temperature is then raisedto 280 C. Acetic acid distils over,

form.

What I claim and desire to secure by Letters Patent is:--

1. The manufacture of oxygenated organic compounds which comprisesthermally decomposing a metal salt of an aliphatic acid in the presenceof an inert high boiling diluent that is liquid at the temperature oftreatment.

2. The manufacture of oxygenated organic compounds which comprisesthermally decomposing a metal salt of a lower fatty acid in the presenceof an inert high boiling diluent that is liquid at the temperature oftreatment.

3. The manufacture of oxygenated organic compounds which comprisesthermally decomposing an' actate of a metal in the presence of an inerthigh boiling diluent that is liquid at the temperature of treatment.

4. The manufacture of oxygenated organic compounds which comprisesthermally decomposing a metal salt of a lower fatty acid in the2,oe1,c15 g 3 compounds which comprises thermally decom- Boiling diluentthat is liquid at such temperatures.

high boiling hydrocarbon that is liquid at the 11. The manufacture ofoxygenated organic temperature of treatment. compounds which comprisesheating an acetate 5 7. The manufacture of oxygenated organic of a metalto a temperature between 200 and 5 compounds which comprises thermallydecom- 450 C. in the presence of an inert high boiling posingan acetateof a metal in the presence or diluent, that is liquid at suchtemperatures. a high boiling ether that is liquid at the tem- 12. Thmanuf ctur f oxy n ed or ni perature of treatment. compounds whichcomprises forming a metal salt 8. The manufacture of oxygenated organicof a lower fatty acid from an aqueous solution 10 the presence of aninert high boiling diluent that and 450 C. in presence of an inert highboiling 15 is liquid at the temperature of treatment. diluent that isliquid at such temperatures. 9. The manufacture of oxygenated organic13. The manufacture of oxygenated organic compounds which comprisesheating to a tempercompounds which comprises forming an actate ature atwhich it thermally decomposes an aceof a metal from an aqueous solutioncontaining tate of a metal in admixture with a normal salt of aceticacid, separating the acetate from the solu- 20 a strong mineral acid inthe presence of an inert tion, removing atleast part of its watercontent high boiling diluent that is liquid at'the temand subjecting theacetate to thermal decomposiq tion at a temperature between 200 and 450C.

I 10. The manufacture of oxygenated organic in presence of an inert highboiling diluent-that 5 compounds which comprises heating a metal salt isliquid at such temperatures.

of a lower fatty acid to a temperature between 200 and 450 C. in thepresence of an inert high I IENRY DREYFUB.

